The invention generally pertains to reflector systems for antenna signal transmitting or receiving systems. More particularly, the invention concerns arranging two reflectors in the same shared aperture space for transmitting or receiving signals which are orthogonally polarized with respect to each other.
Conventional energy radiating systems such as antenna systems typically use feed horns to radiate energy off a reflector, typically of parabolic surface contour. Such reflectors are used to collimate or focus the beam of energy for increased radiation efficiency. This arrangement is analogous to a flashlight or searchlight having a reflective curved surface behind the light source itself for increasing the intensity of the output beam.
Energy waves, for example in the radio frequency spectrum, typically are polarized having two orthogonal components--one conventionally termed horizontal the other vertical. Hence it has been possible to broadcast two different signals at the same operating frequency of the radiated energy wherein one signal is derived from the horizontally polarized component and the second signal derived from the vertically polarized component of the energy wave.
In known systems, the two orthogonal components are used to double the information sent at the same frequency by using two separate antennas. The separate antennas generate signals which are orthogonally polarized at the same frequency. In subsequent prior art arrangements, two reflectors for the two antennas were used but placed one behind the other, where the reflectors had grids built into their surfaces such that one reflector would reflect only signals of a first polarity while the other reflector would reflect only signals of the second polarity. In such prior systems, each reflector has its own focal point. The feed horns for the respective polarized signals are located in the vicinity of the focal points, and since such feed horns may not occupy the same physical location, the reflectors necessarily were fashioned of slightly different shapes such that the focal points would not converge along a common focal axis. In known arrangements, the two reflectors would be offset such that the focal axes of the two antennas would be the same, but the focal points would be longitudinally offset along the focal axis. As viewed from the earth, for example, in a satellite communication system carrying the antenna system, the two reflective surfaces in the prior arrangement would be located one behind the other, thus sharing an aperture.
A disadvantage of the prior approach described above is the requirement for increased storage space due to the manner in which the feed systems for the respective orthogonal signals had to be stowed in a spacecraft. Additionally, since the focal points were at differing locations with respect to the center portion of the reflectors, the respective signals were not reflected in an equal manner thereby leading to non-equal performance between the orthogonal pair of polarized signal outputs or inputs. An additional disadvantage of the prior approach is the non-symmetrical arrangement required for the two reflectors resulting in a large variation in total reflector assembly thickness from one edge of the shared aperture to the other. Such large variations in thickness, in turn, lead to problems in stowage of the non-deployed deflector systems in many typical spacecraft having a minimum of available volume for accommodating the reflector system.